Gabriel Aguilera

Performance of MIMO MRC Systems with Co-Channel Interference

We determine exact closed-form expressions for the outage probability of multiple-input/multiple-output systems in Rayleigh fading with maximal ratio diversity combining and co-channel interference. Our analysis generalizes prior work in that we place no restrictions on the number or power of the interferers, or on the number of antennas at the transmitter and receiver. We also present an alternative mathematical approach to performance analysis that leads to an undemanding expression for the SINR moment generating function, which can then be used to evaluate average probability of error and the moments of the SINR. Our numerical results indicate that, for a fixed total interference power, system performance degrades when there are dominant interferers. In addition, for a fixed total number of transmit and receive antennas, outage probability and average bit error rate decrease when the transmitter and receiver have the same number of antennas.

Closure via functional dependence simplification

In this paper, a method for computing the closure of a set of attributes according to a specification of functional dependencies of the relational model is described. The main feature of this method is that it computes the closure using solely the inference system of the SL FD logic. For the first time, logic is used in the design of automated deduction methods to solve the closure problem. The strong link between the SL FD logic and the closure algorithm is presented and an SL FD simplification paradigm emerges as the key element of our method. In addition, the soundness and completeness of the closure algorithm are shown. Our method has linear complexity, as the classical closure algorithms, and it has all the advantages provided by the use of logic. We have empirically compared our algorithm with the Diederich and Milton classical algorithm. This experiment reveals the best behaviour of our method which shows a significant improvement in the average speed.

Performance comparison of MRC and IC under transmit diversity

This work explores the performance of MIMO (multiple-input/multiple-output) systems in Rayleigh fading channels with co-channel interference (CCI) and thermal noise. We provide analytical expressions for the outage probability of maximal ratio transmission combined with one of two different receive antenna array schemes, maximal ratio combining (MRC) and interference cancellation (IC) via null steering of the array pattern. We derive the statistics of the signal to interference-plus- noise ratio (SINR) for each technique in a closed-form and obtain an integral expression to calculate the average bit error rate (BER) or symbol error rate (SER). Our results show the conditions under which IC yields significantly better performance than MRC and vice versa. We also determine the impact on performance of the number of antennas in the transmit array.

Reductions for non-clausal theorem proving

This paper presents the TAS methodology as a new framework for generating non-clausal Automated Theorem Provers. We present a complete description of the ATP for Classical Propositional Logic, named TAS-D, but the ideas, which make use of implicants and implicates can be extended in a natural manner to first-order logic, and non-classical logics. The method is based on the application of a number of reduction strategies on subformulas, in a rewrite-system style, in order to reduce the complexity of the formula as much as possible before branching. Specifically, we introduce the concept of complete reduction, and extensions of the pure literal rule and ofthe collapsibility theorems; these strategies allow to limit the size ofthe search space. In addition, TAS-D is a syntactical countermodel construction. As an example of the power of TAS-D we study a class of formulas which has linear proofs (in the number of branchings) when either resolution or dissolution with factoring is applied. When applying our method to these formulas we get proofs without branching. In addition, some experimental results are reported. Copyright 2001 Elsevier Science B.V.

Reducing signed propositional formulas

Abstract New strategies of reduction for finite-valued propositional logics are introduced in the framework of the TAS1 methodology developed by the authors [1]. A new data structure, the Δ^-sets, is introduced to store information about the formula being analysed, and its usefulness is shown by developing efficient strategies to decrease the size of signed propositional formulas, viz., new criteria to detect the validity or unsatisfiability of subformulas, and a strong generalisation of the pure literal rule.

A Non-explosive Treatment of Functional Dependencies Using Rewriting Logic

The use of rewriting systems to transform a given expression into a simpler one has promoted the use of rewriting logic in several areas and, particularly, in Software Engineering. Unfortunately, this application has not reached the treatment of Functional Dependencies contained in a given relational database schema. The reason is that the different sound and complete axiomatic systems defined up to now to manage Functional Dependencies are based on the transitivity inference rule. In the literature, several authors illustrate different ways of mapping inference systems into rewriting logics. Nevertheless, the explosive behavior of these inference systems avoids the use of rewriting logics for classical FD logics. In a previous work, we presented a novel logic named SL FD whose axiomatic system did not include the transitivity rule as a primitive rule.

An accelerated-time simulation of car traffic on a motorway using a CAS

In this paper we introduce a new model, called the GRAM model, that provides an accelerated-time simulation of traffic on a motorway. The model provides an accelerated-time simulation using ideas and techniques from both cellular automata and neural network models. It has been implemented in a package using a Computer Algebra System (CAS) for the development of algorithms and a Java environment to display the simulated results graphically.

TAS-D++: Syntactic Trees Transformations for Automated Theorem Proving

In this work a new Automated Theorem Prover (ATP) via refutation for classical logic and which does not require the conversion to clausal form, named TAS-D++, is introduced. The main objective in the design of this ATP was to obtain a parallel and computationally efficient method naturally extensible to non-standard logics (concretely, to temporal logics, see [8]).

MAT logic: a temporal×modal logic with non-deterministic operators to deal with interactive systems in communication technologies

In this paper, the Multi-flow Asynchronous Temporal Logic, called MAT Logic, is presented. MAT Logic is a new temporal×modal logic with non-deterministic operators among time flows as accessibility relations. The main goal of this work has been the design and description of a logic that could be capable of managing communications among systems with not necessarily synchronizable time flows. In order to better understand the design of the logic, an example in the field of communications is given.

A logic with imprecise probabilities and an application to automated reasoning using rewriting techniques

A new probabilistic logic for handling imprecise probabilities is introduced, implemented in a rewriting system, and used to carry out an experiment. Each well-formed formula of the probabilistic logic is labeled with two values that represent possible minimum and maximum probabilities associated with the event related to the unlabeled formula. The aim of this logic is to facilitate application of rules to obtain an approximation of the probability interval associated with an event, without the necessity of knowing the precise probability of other events. The logic is described as a formal theory by means of its language, semantics and a proof theory. The soundness of the proof theory has been proven. Rewriting techniques are a powerful method for testing the behavior of a formal proof calculus through translation of calculus inference rules into rewrite rules. Implementation of the logic rules in a rewriting language such as Maude allows an automated reasoning system to be easily obtained, which can be consulted by applications. We developed a small game application and an experiment to test the application.